In lithography, there is an ongoing desire to reduce the size of features in a lithographic pattern in order to increase the density of features on a given substrate area. In photolithography, the push for smaller features has resulted in the development of technologies such as immersion lithography and extreme ultraviolet (EUV) lithography, which are however rather costly.
A potentially less costly road to smaller features (e.g. micron size or nanometer sized features, e.g., less than or equal to 10 microns, less than or equal to 1 micron, less than or equal to 50 nm, less than or equal 25 nm or less than or equal to 10 nm sized features) that has gained increasing interest is so-called imprint lithography, which generally involves the use of a “stamp” (often referred to as an imprint lithography template) to transfer a pattern onto a substrate. An advantage of imprint lithography is that the resolution of the features is not limited by, for example, the emission wavelength of a radiation source or the numerical aperture of a projection system. Instead, the resolution is mainly limited to the pattern density on the imprint lithography template.
Imprint lithography involves the patterning of an imprintable medium on a surface of a substrate to be patterned. The patterning may involve bringing together a patterned surface of an imprint lithography template and a layer of imprintable medium (e.g., moving the imprint lithography template toward the imprintable medium, or moving the imprintable medium toward the imprint lithography template, or both) such that the imprintable medium flows into recesses in the patterned surface and is pushed aside by protrusions on the patterned surface, to adopt the topography of that patterned surface. The recesses define pattern features of the patterned surface of the imprint template. The patterned features may have features having dimensions of the order of micrometers or nanometers. Typically, the imprintable medium is flowable when the patterned surface and the imprintable medium are brought together. Following patterning of the imprintable medium, the imprintable medium is suitably brought into a non-flowable or frozen state (i.e. a fixed state), for example by illuminating the imprintable medium with actinic radiation. The patterned surface of the imprint lithography template and the patterned imprintable medium are then separated. The substrate and patterned imprintable medium are then typically processed further in order to pattern or further pattern the substrate (e.g. by etching or the like). The imprintable medium may be provided in the form of droplets on the surface of a substrate to be patterned, but may alternatively be provided using spin coating or the like.
In order to fix a pattern provided in a layer of imprintable medium by an imprint lithography template, a number of options are available. One option involves heating of the imprintable medium to fix the pattern provided in that medium by the imprint lithography template. Another option involves the use of irradiation of the imprintable medium with actinic radiation. In order to provide such actinic radiation, a source of actinic radiation is in connection with the imprint lithography apparatus, or forms part of that imprint lithography apparatus. A UV laser could be used to provide the actinic radiation.